A commonly used method for implanting metallic implants into bone tissue is a two stage procedure involving in a first operation surgically placing the implant into the bone tissue, where it is then allowed to rest unloaded and immobile for a healing period of three months or more in order to allow the bone tissue to grow onto the implant surface so as to permit the implant to be well attached to the bone tissue, the cut in the soft tissue covering the implant site being allowed to heal over the implant, and in a second operation opening the soft tissue covering the implant and attaching the functional parts to the implant. This two-stage procedure is often used in connection with dental implants, one reason being that it minimized the risk of infection of the implant site from the oral cavity. In some orthopedic applications the above two-stage surgery may not be necessary since most orthopaedic implants do not penetrate the soft tissue. A prolonged healing period is however still considered necessary since any movements of the implant in the weeks and months following surgery may endanger the final attachment of the implant to the bone tissue.
The above procedure is for instance described in Brånemark et al: “Osseointegrated Implants in the Treatment of Edentulous Jaw, Experience from a 10-year period”, Almquist & Wiksell International, Stockholm-Sweden.
However, the fact that the implant may not be loaded means that the functional parts of the implant may not be attached to the implant and/or used during the healing period of three months or more. In view of the discomfort associated with this, it is desirable to minimize the time period necessary for the above-mentioned first stage and in some cases, for instance in certain orthopaedic application, substantially dispense with said first stage and perform the entire implantation procedure in a single operation.
An object of the present invention is to provide an implant with improved rate of bone tissue attachment such that the post-surgery healing period described above may be reduced.
Some of the metals or alloys used for bone implants are capable of forming a strong bond with the bone tissue, a bond which may be as strong as the bone tissue per se, sometimes even stronger. The most notable example of this kind of metallic implant material is titanium and allows of titanium whose properties in this respect have been known since about 1950. This bond between the metal and bone tissue has been termed “oseointegration” by Brånemark et al.
Although this bond between titanium and bone tissue is comparatively strong, in some applications it is desirable to enhance the bond between metal and bone tissue.
There are to date several methods for treating implants made of titanium in order to obtain a better attachment of the implant. Some of these involve altering the topography of the implant, for example by creating relatively large irregularities on the implant surface in order to obtain a better mechanical retention and to increase the area of attachment, by for example plasma spraying, blasting or etching. Although the retention may be improved, the time necessary for the osseointegration process may be longer since the bone tissue would have to grow into the irregularities in the surface.
Other methods involve altering of the chemical properties of the implant surface. For example one such method involves the application of a layer of ceramic material such as hydroxyapatite to the implant surface, inter alia in order to stimulate the regeneration of the bone tissue. Ceramic coatings however may be brittle and may flake or break off from the implant surface, which may in turn lead to the ultimate failure of the implant.
U.S. Pat. No. 4,330,891 could perhaps be said to combine each of the above, in that the provision of an element with a micro-pitted surface which micro-pits are within a certain diameter range, is said to effect improved properties as regards acceptance of the carrier element, and primarily improved durability of the healthy ingrowth of the element due to its biological quality.
A further object of the invention is to provide an implant forming a stronger bond with the bone tissue.